Geoscience Reference
In-Depth Information
Mariotte
buret
three-way valve
B
A
stopper
water
supply
tensiometer
z
top
H
in
z
1
water
manometer
SOIL
O-ring
porous plate
H
1
z
2
z
bot
H
2
H
out
graduated
cylinder
Figure 4.31
Experimental setup to measure hydraulic conductivity at small tensions
(Dirksen,
1999
).
initial and boundary conditions, accuracy of measurements, error propagation in data
analysis, range of application, duration of method, equipment and check on measure-
ments (Dirksen,
1999
).
In case of hysteresis in the
θ
(
h
) relation (
Figure 4.15
), the
k
(
h
) relation will also
show hysteresis. As the hydraulic conductivity is mainly determined by the water
content,
k
(
θ
) relations show only minor hysteresis and are therefore preferred above
k
(
h
) relations.
Figure 4.31
shows an experimental setup for measuring hydraulic conductivity
at small tensions. Steady hydraulic head gradients are imposed on a sand column
by a Mariotte buret at the inlet and a drip point at the outlet. The hydraulic gradient
within the vertical soil column is measured with tensiometers connected to water
manometers. Unit hydraulic gradient (gravitational low) resulting in uniform water
content can be obtained by gradually adjusting the externally imposed hydraulic
heads.
The soil column is clamped between two porous plates. These plates are needed to
keep air out of the tubes, which are illed with water at
h
< 0! The air entry value of
the porous plates and tensiometers should be small (about -20 cm) to have a highly
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